The present invention pertains to velocimeters. In particular, the invention pertains to noninvasive velocity sensing of gas flow. More particularly, the invention is a gas velocimeter that utilizes fluorescence in sensing techniques.
Present techniques for air data measurement mainly rely on external probes, such as in aircraft, to measure total and static pressures and temperatures which are used to derive required air data parameters. In certain environments, such as high speed aircraft or spacecraft, such probes are impractical where the invasive nature of the probe results in severe heating of the probe and ultimate destruction of the probe. In advanced supersonic and hypersonic flights of aircraft, the energy of the gas or air flow is sufficient to result in a prohibitively high rate of heat deposition on the probe.
Military missions often require aircraft having minimum radar and electro-optic scattering cross sections. These cross sections are significantly increased by the use of external probes. The present invention is physically noninvasive as no types of external probes are required. Only moderate levels of laser power are used to interrogate the flow of atmosphere gases. Thus, the invention provides increased military or space survivability when compared with conventional velocimeters.
Other art, such as advanced optical devices, has been developed to attain noninvasive measurement of gas flow parameters. Most of these devices rely on the scattering of photons from particles within the flow being measured. The latter devices include laser velocimeters in the present art. However, such devices are unattractive for use at high altitudes because the density of particles of appropriate size satisfactory for device operation decreases rapidly with altitude.
The present invention is much less sensitive to such density decrease of particles, since it relies on inelastic scattering from molecular constituents within the flow.